Assembly of an instrument system for dynamic quantitative microspectrofluorimetry is proposed. By combining acquired components with our existing developmental apparatus a unique instrument system capability will be achieved for sensitive biophysical studies. It will provide: (1) fluorescence photobleaching recovery (FPR) and fluorescence correlation spectroscopy (FCS) capability for measurement of lateral motion on cell surfaces, (2) video intensifier microscopy images at high quantum efficiency to observe fluorescent molecular marker redistribution as the architecture of living cells develops, (3) quantitative video intensity discrimination at high intensity resolution to detect small changes of membrane potential with the help of fluorescent potential sensing dyes, (4) signal averaging analysis of weak fluorescence signals in order to measure the dynamics of membrane receptors on cells and in vesicles. This instrument system is to be applied to studies of the dynamics of cell membrane processes, development of interneuronal communication, motor end plate activity, acetylcholine receptor mechanisms, and other problems of cell membrane biophysics as detailed herein.